Method of forming a brilliant multi-layered coating film

Abstract

This invention provides a method for forming brilliant multi-layered coating film excelling in brilliance, which comprises the steps of applying an effect pigment-containing water-borne base coating composition (A1) having a coating film viscosity (V A1 ) after 1 minute of its application of 10-500 Pa·sec onto a substrate to form a first base coating film; and applying an effect pigment-containing water-borne base coating composition (A2) having a coating film viscosity (V A2 ) after 1 minute of its application of 5-200 Pa·sec onto the first base coating film while the viscosity (V A3 ) of the first base coating film is 10-500 Pa·sec, the viscosity ratio (V A1 )/(V A2 ) being 1.3/1-35/1.

The invention claimed is: 
     
       1. A method for forming a brilliant multi-layered coating film, which comprises the steps of
 (1) applying an effect pigment-containing water-borne base coating composition (A1) onto a substrate to form a first base coating film, 
 (2) applying an effect pigment-containing water-borne base coating composition (A2) onto the uncured first base coating film to form a second base coating film, and 
 (3) heat-curing the two coating films, wherein 
 (i) the effect pigment-containing, water-borne base coating composition (A1) has a viscosity (V A1 ), as measured under the conditions of shear rate of 0.1 sec −1  and 23° C. in temperature, at one minute after its application, within a range of 10-500 Pa·sec; 
 (ii) the effect pigment-containing water-borne base coating composition (A2) has a viscosity (V A2 ), as measured under the conditions of shear rate of 0.1 sec −1  and 23° C. in temperature, at one minute after its application, within a range of 5-200 Pa·sec; 
 (iii) the ratio between the viscosities, (V A1 )/(V A2 ), lies within a range of 1.3/1-22.5/1; and 
 (iv) the effect pigment-containing water-borne base coating composition (A2) is applied while the viscosity (V A3 ) of the first base coating film, as measured under the conditions of shear rate of 0.1 sec −1  and 23° C. in temperature, is within a range of 10-500 Pa·sec; and 
 (v) the viscosity (V A1 ) of effect pigment-containing, water-borne base coating composition (A1) is optionally controlled by blending a rheology-controlling agent with the composition (A1), and the viscosity (V A2 ) of effect pigment-containing, water-borne base coating composition (A2) is controlled by blending a rheology-controlling agent with the composition (A2), wherein the rheology-controlling agent in composition (A1) may be the same or different from the rheology-controlling agent in composition (A2). 
 
     
     
       2. The method according to  claim 1 , in which the effect pigment-containing water-borne base coating composition (A1) has a viscosity (V A1 ) at one minute after its application within a range of 30-250 Pa·sec, as measured under the conditions of shear rate of 0.1 sec −1  and temperature of 23° C. 
     
     
       3. The method according to  claim 1 , in which the effect pigment-containing water-borne base coating composition (A2) has a viscosity (V A2 ) at one minute after its application within a range of 8-80 Pa·sec, as measured under the conditions of shear rate of 0.1 sec −1  and temperature of 23° C. 
     
     
       4. The method according to  claim 1 , in which the ratio of the viscosities, (V A1 )/(V A2 ) is within a range of 2/1-22.5/1. 
     
     
       5. The method according to  claim 1 , in which the effect pigment-containing water-borne base coating composition (A2) is applied while the viscosity (V A3 ) of the first base coating film is within a range of 30-250 Pa·sec, as measured under the conditions of shear rate of 0.1 sec −1  and temperature of 23° C. 
     
     
       6. The method according to  claim 1 , in which the effect pigment-containing water-borne base coating composition (A1) and effect pigment containing water-borne base coating composition (A2) are water-borne coating compositions comprising water-soluble or water-dispersible main resin (a), curing agent (b) and effect pigment (c). 
     
     
       7. The method according to  claim 6 , in which the main resin (a) is acrylic resin or polyester resin containing carboxyl groups and hydroxyl groups. 
     
     
       8. The method according to  claim 6 , in which the effect pigment (c) is contained within a range of 2-50 mass parts per 100 mass parts of the combined solid contents of the main resin (a) and the curing agent (b). 
     
     
       9. The method according to  claim 1 , in which the effect pigment-containing water-borne base coating composition (A1) further contains inorganic fine particles having an average primary particle diameter not greater than 1 μm. 
     
     
       10. The method according to  claim 9 , in which the pigment mass concentration of the inorganic fine particles is within a range of 2-30%. 
     
     
       11. The method according to  claim 9 , in which the inorganic fine particles are barium sulfate fine particles. 
     
     
       12. The method according to  claim 1 , in which the effect pigment-containing water-borne base coating composition (A1) and effect pigment-containing water-borne base coating composition (A2) contain barium sulfate fine particles having an average primary particle diameter not greater than 1 μm, and the pigment mass concentration (%) of the barium sulfate fine particles contained in the effect pigment-containing water-borne base coating composition (A1) is higher than the pigment mass concentration (%) of the barium sulfate fine particles contained in the effect pigment-containing water-borne base coating composition (A2) by at least 5%. 
     
     
       13. The method according to  claim 6 , in which the curing agent (b) is an amino resin. 
     
     
       14. The method according to  claim 1 , in which the effect pigment-containing water-borne base coating compositions (A1) and (A2) contain melamine resin, the weight-average molecular weight (M A1 ) of the melamine resin contained in the effect pigment-containing water-borne base coating composition (A1) is within a range of 800-5,000; the weight-average molecular weight (M A2 ) of the melamine resin contained in the effect pigment-containing water-borne base coating composition (A2) is within a range of 400-4,000; and the weight-average molecular weight (M A1 ) of the melamine resin contained in the effect pigment-containing water borne base coating composition (A1) is larger than the weight-average molecular weight (M A2 ) of the melamine resin contained in the effect pigment-containing water-borne base coating composition (A2) by 300-4,000. 
     
     
       15. The method according to  claim 1 , in which the effect pigment-containing water-borne base coating compositions (A1) and (A2) contain at least one kind of alkyl etherified melamine resin selected from the group consisting of methyl etherified melamine resin, butyl etherified melamine resin, and methyl-butyl mixed etherified melamine resin; and the molar ratio (mol %) of the butyl group to the sum of mol numbers of methyl and butyl groups in the alkyl etherified melamine resin contained in the effect pigment-containing water-borne base coating composition (A1) is greater than the molar ratio (mol %) of the butyl group to the sum of mol numbers of the methyl and butyl groups in the alkyl etherified melamine resin contained in the effect pigment-containing water-borne base coating composition (A2) by at least 30%. 
     
     
       16. The method according to  claim 1 , in which the effect pigment-containing water-borne base coating compositions (A1) and (A2) contain alkyl etherified melamine resins, the alkyl etherified melamine resin contained in the effect pigment-containing water-borne base coating composition (A1) being methyl-butyl mixed etherified melamine resin and/or butyl etherified melamine resin, and that contained in the effect pigment-containing water-borne base coating composition (A2) being methyl etherified melamine resin. 
     
     
       17. The method according to  claim 1 , in which the solid content (S A1 ) of the effect pigment-containing water-borne base coating composition (A1) is within a range of 15-45 mass %, and the solid content (S A2 ) of the effect pigment-containing water-borne coating composition (A2) is within a range of 5-30 mass %, the ratio, S A1 /S A2 , of the solid content (S A1 ) of the effect pigment-containing water-borne base coating composition (A1) to the solid content (S A2 ) of the effect pigment-containing water-borne base coating composition (A2) is within a range of 1.5/1-5/1. 
     
     
       18. The method according to  claim 1 , in which the solid content (S A1 ) of the effect pigment-containing water-borne base coating composition (A1) is within a range of 20-39 mass % and the solid content (S A2 ) of the effect pigment-containing water-borne base coating composition (A2) is within a range of 7-9 mass %, the ratio, S A1 /S A2 , of the solid content (S A1 ) of the effect pigment-containing water-borne base coating composition (A1) to the solid content (S A2 ) of the effect pigment-containing water-borne base coating composition (A2) is within a range of 2.6/1-4.5/1. 
     
     
       19. The method according to  claim 1 , in which the ratio, T A1 /T A2 , of the dry film thickness (T A1 ) of the coating film formed of the effect pigment-containing water-borne base coating composition (A1) to the dry film thickness (T A2 ) of the coating film formed of the effect pigment-containing water-borne base coating composition (A2) is within a range of 1.5/1-5/1. 
     
     
       20. The method according to  claim 19 , in which the dry film thickness of the coating film formed of the effect pigment-containing water-borne base coating composition (A1) is within a range of 5-15 μm, and that of the coating film formed of the effect pigment-containing water-borne base coating composition (A2) is within a range of 1-5 μm. 
     
     
       21. The method according to  claim 1 , in which the substrate is a car body on which electrodeposition coating and intermediate coating have been applied by the order stated. 
     
     
       22. The method according to  claim 1 , comprising applying a clear coating composition onto the uncured second base coating film, and thereafter heating to cure the first base coating film, the second base coating film and the clear coating film simultaneously. 
     
     
       23. The method according to  claim 13 , wherein the amino resin is a melamine resin.